Time delay fuse

ABSTRACT

A time delay fuse which is particularly adapted to eliminate failures during a short circuit test. The device uses a high refracting silicon material admixed with a metallic salt which acts as the heat sink. This material replaces the usual additional fusable metal, but will not dissolve or vaporize during a short circuit. Pressures are reduced and the fuse will not burst or otherwise fail.

United States Patent Inventor Paul P. Danesl Attleboro Falls, Mass.App]. No. 4,380 Filed Jan. 20, 1970 Patented Sept. 28, 1971 AssigneeCable Electric Products Inc. Providence, RJ.

TIME DELAY FUSE 3 Claims, 4 Drawing Figs.

U.S. Cl 337/166, 3 37/ l 85 lnt.Cl .H01h85/10, l-lOlh 85/62 Field ofSearch 337/163,

References Cited UNITED STATES PATENTS 2,557,587 6/1951 Baenziger337/166 2,506,304 5/1950 Ludwig 337/166 2,326,257 8/1943 Schmidt et al.337/166 2,302,820 ll/l942 Von Liemdt 337/296 X Primary Examiner--BernardA. Gilheany Assistant Examiner-Dewitt M. Morgan Attorney- Max SchwartzABSTRACT: A time delay fuse which is particularly adapted to eliminatefailures during a short circuit test. The device uses a high refractingsilicon material admixed with a metallic salt which acts as the heatsink. This material replaces the usual additional fusable metal, butwill not dissolve or vaporize during a short circuit. Pressures arereduced and the fuse will not k gL mt ihsiwisq f l PATENIEDSEP28IBYI3.609.621

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v INVENTOR PAUL P. DANESI ATTO N EY TIME DELAY FUSE My present inventionrelates to the electrical art, and more particularly to a time delayfuse.

The principal object of the present invention is to provide a time delayfuse which reduces the volume of fusable material in the fuse.

Another object of the present invention is to provide a time delay fusewhich replaces some of the fusable material in the fuse with a highrefractory nonfusable material.

A further object of the present invention is to provide a time delayfuse which will easily pass the Underwriters short circuit test byreducing the internal pressures in the fuse.

' A further object of the presentinvention is to provide a time delayfuse with a novel heat sink material which is simple and easy to applyto the fuse.

Another object of the present invention is to provide a novel time delayfuse which is simple in construction and easy and economical tomanufacture and assemble.

With the above and other objects and advantageous features in view, myinvention consists of a novel arrangement of parts, more fully disclosedin the detailed description following, in conjunction with theaccompanying drawings, and more particularly defined in the appendedclaims.

In the drawings,

FIG. 1 is a vertical section of an S type time delay fuse embodying myinvention;

FIG. 2 is a side elevation of the fusable link therefore;

FIG. 3 is a top plan view of the link; and

FIG. 4 is a side elevation of a fusable link for a standard type fuse.

It is good practice to provide some fuses with a time delay action toprevent unnecessary blowouts. For example, washing machine motors,starting under a heavy load, will draw more than the safe amperage butwill then settle down while running. To prevent the fuse from blowingimmediately, a time delay is provided. This is usually accomplished byadding an additional piece of metal to the fuse link, at one side, whichacts as a heat sink and will draw off the initial heat to delay theburning out of the fuse. The Underwriters Laboratories require that suchfuses give'out in a minimum of 12 seconds and maximum of 2 minutes.However, such fuses must also pass a short circuit test. This testsuddenly pushes 10,000 amps@ 125 v. AC through the fuse. The link notonly melts but vaporizes. Pressures build up within the body of thefuse. The test requires the fuse to hold without bursting or blowing offthe cover or otherwise leaking the hot vaporized gases.

It is obvious that the time delay fuse, with its additional metal heatsink, builds up heavier pressures in this test than the standard fuse.The present invention provides a time delay fuse in which the heat sinkcomprises a nonfusable material thus not only not adding to thevaporized mass, but the material also encompasses some of the fusablematerial to actually reduce the pressures in the fuse to less than in astandard type fuse.

Referring more in detail to the drawings, the fuse shown in FIG. 1 isthe new type S. The body portion is made of unglazed porcelain with themain threaded portion 11 and an enlarged head 12. The head 12 has anannular chamber with an auxiliary wall portion 13 at one side. Thecontact elements are made of copper alloy. The hollow body 14, extendingthrough the portion 11, terminates in a restricted opening 15 whichflares outwardly at the outer end 16. A hollow copper alloy contactelement 17 is mounted in this end. It is formed like a hollow rivet,with its outer end flattened at 18 to form the bottom contact. Itextends upwardly and flares out against the wall at l9 to be locked inplace.

The second contact element is also copper alloy and is in the form of ahorseshoe shape 20 having a downwardly extending resilient contactportion 21 (dotted lines). This contact element 20 is positionedsurrounding the upper end of the body portion 11 just below the head 12.

The fuse link 22, see FIGS. 2 and 3, is of a conventional fusable metalsuch as zinc. The link 22 has a short vertical portion 23 and then turnsslightly to the left (FIG. 2) and then upwardly to form a long verticalleg 24. At the upper end it IS reentrantly bent to form a loop 25 and ashort spaced parallel vertical leg 26. It then turns sharply to theright at a slight upward angle to form the link portion 27. Then thereis another shorter upward and downward form to make the loop 28 at theright. As can be seen in FIG. 3, the fuse link 22 is flat andribbonlike. At the link portion 27, it is tapered down at 29 to reducethe metallic conductive area and provide the fusable point of thedevice.

The fuse link 22 is mounted in the body 10 as shown in FIG. 1. The shortbottom portion 23 enters the contact element 17 and the bottom end issoldered or otherwise electrically attached to it. The link ispositioned at an angle to the left (FIG. 1) to allow sufficient room forthe fusable portion 27. The short end loop 28 is mounted over the top ofthe auxiliary wall 13 and the free end of the link extends downwardlythrough an opening in the body 10 to contact the element 20 at thispoint. The element 20 is also provided with a tab portion 30 whichextends through this opening to make the contact. A porcelain or otherhigh refractory material 31 is poured into the space behind theauxiliary wall 13 to seal the opening, lock the link in place, and sealthe contact between the link and the element 20.

All of the above construction is fairly standard. However, in accordancewith the present invention, 1 now provide the link 22 with a time delayheat sink. This comprises a high refractory silicon material admixedwith a metallic salt. The silicon itself, being a ceramic material,would not absorb any heat fast enough to form the necessary heat sink.However, applicant has found that the addition of a metallic salt willrender it heat absorptive at a much higher rate. Furthermore, the ratecan be controlled by the proportion of salt to the silicon. For example,a 50-5 proportion by volume will form a mixture which will satisfy theUnderwriters tests. The mixture is positioned on the loop portion 25 asshown in FIG. 1 and in dotted lines in FIG. 2. The mixture 32 extendsdownwardly to cover all of the vertical leg 26 of the link, the parallelportion of the leg 24, and part of the fusable link portion 27.

Since it is close to the fusable link portion 29, its heat sink effectwill act as the necessary time delay for the fuse. However, it will notvaporize during the short circuit tests and will prevent the materialwithin it from vaporizing, thus, actually reducing the amount ofvaporizable material in the fuse.

FIG. 4 shows the application of the present invention to a regular typefuse. Here the fuse link 33 is provided with the horizontal fusableportion 34 and two short loops 35 at each end. The material 36 ismounted to enclose the loops 35 to form a heat absorbing mass at eachend of the link portion 34.

The present invention thus provides a heat sink material for a timedelay fuse which replaces the metal now in use. This material not onlyis effective as a heat sink but is nonfusable and nonvaporizing toensure the safety of the fuse and its ability to pass the short circuittests. Other advantages of the present invention will be readilyapparent to a person skilled in the art.

Iclaim:

l. A time delay fuse comprising a porcelain housing, a fuse link mountedin said housing adapted to fuse under the excessive heat of a shortcircuit, said link comprising a thin ribbon of zinc material, and a massof nonfusable material mounted on said link to absorb the heat and delaythe fusing action of said link, said nonfusable material comprising ahigh refractory silicon admixed with a metallic salt in a predeterminedpro portion to control the time of the delay.

2. A time delay fuse as in claim I, wherein said link is provided withan integral loop adjacent one end of the fusable portion of said link,said mass of nonfusable material encompassing said loop and a portion ofsaid link fuse material.

3. A time delay fuse as in claim 2, wherein said high refractory siliconis admixed with a metallic salt in a 50-50 ratio.

2. A time delay fuse as in claim 1, wherein said link is provided withan integral loop adjacent one end of the fusable portion of said link,said mass of nonfusable material encompassing said loop and a portion ofsaid link fuse material.
 3. A time delay fuse as in claim 2, whereinsaid high refractory silicon is admixed with a metallic salt in a 50-50ratio.